Telephone system



Dec. 17, 1929. T. F. CROCKER ET AL TELEPHONE SYSTEM Filed March 21, 1927 Imren ur's Thomas Fl ruckar and Harry K. Pars hall 7 Wm Patented Dec. 17, 1929 UNETE STATES PATENT OFFIQ THOMAS F. CROCKER AND HARRY R. PARSHALL, OF CHICAGO, ILLINOIS, ASSIGNOES T0 RESERVE HOLDING COMPANY, OF KANSAS CITY, MISSOURI, A CQRPORATIOIJ OF DELAWARE TELEPHONE SYSTEM Application filed March 21, 1927. Serial No. 176,868.

The present invention relates to telephone systems in general, but is concerned more particularly with methods of establishing so called two number toll connections be tween a number of automatic exchanges located in adjacent towns or cities within a certain area.

In order to provide efiicient toll service between the adjacent towns, the automatic exchange which is best located for this purpose is equipped with a toll switchboard where the toll or trunk lines to the automatic exchanges in the adjacent towns terminate, and by means of which a toll operator at the toll switchboard may complete so called two number toll connections between automatic subscribers in any two of the automatic ex changes. The principal object of the invention is the provision of a new and improved two way trunk circuit for use under these circumstances.

One feature of the invention is the provision of a trunk circuit having separate answering and call jacks with separate sleeve conductors by means of which the trunk circuit is automatically adjusted for either incoming or outgoing service dependent upon whether the answering jack or a multiple call jack has been plugged into.

It is a further object to provide a high re sistance by-path or shunt around the condensers of the trunk circuit in order to give high resistance supervision to the cord circuit, at the same time preventing over saturation of the retard coil which is bridged across the cord circuit, and also to provide means for removing the high resistance bypath or shunt when high resistance supervision is not required.

According to another feature of the invention, the high resistance by-path around the condensers of the trunk circuit prevents the occurrence of false impulses due to momentary making and breaking contact while the plug is being inserted into the ack by rendering the line switch associated with the trunk circuit inoperative until after the plug is fully inserted and until the dial key of the cord circuit has been operated.

Accordin'g to another feature of the invention, the high resistance by-path and the 0011- densers of the trunk circuit are both shunted out during the time the operator is dialling over the trunk circuit.

According to a further feature of the invention two similar trunk circuits, one incoming and the other outgoing, may be connected by a cord circuit having no condensers and the circuits in only one of the trunk circults will be automatically adjusted to separate the battery feed which is connected to both the incoming and outgoing trunks.

Referring now to the drawings, there is shown by means of the usual circuit diagrams sufficient of the apparatus used to enable the invention to be described and understood.

In the lower left hand corner of the drawing there is shown the improved two way trunk circuit TC terminating at one end at the toll switching center in a multiple call jack DJ and an individual answering jack AJ. The other end of the trunk circuit terminates at a distant automatic exchange in the line switch LS and rotary connector bank contacts 46, 47 and 48. Each trunk circuit such as TC is provided with only one answering ack AJ and is also provided with a plurality of call jacks DJ which are inultipled to the various operators positions in the toll switchboard. Relays are also shown in the trunk circuit, the circuits of which in combination with the sleeve conductors of the answering and calling jacks permit special. operating features to be performed.

The line switches such as LS are located in the distant automatic exchanges and have access to the regular trunking arrangement for completing calls to automatic subscribers in such exchanges. The automatic subscribers have access to the trunk circuits such as TO by way of the rotary connector bank contacts such as 46 to 48, inclusive.

The line switch LS is of the usual non re-- storing or rotary type of line switch while the rotary connectors (not shown) are of the well known Strowger type.

The cord circuit CC shown in the upper half of the drawing is located at the toll switching center and is a double plug ended cord circuit of the universal type. In the cord circuit there is provided two ringing keys, two dialling keys, a monitoring key, a listening key, and a number of relays. Either plug of the cord circuit is adapted to be inserted into either of the jacks of the trunk circuit. The cord circuit shown is more complicated than need be to understand the pre ent invention but as said the cord circuit is also used for connecting with the jacks (not shown) of long distance toll lines and other types of lines, the same has been shown without change. The circuits of a majority of relays in the cord circuit per'l'orm no useful function in the present invention and therefore will not be described.

"With this general description ofthe drawings in .mind, a brief description willnow be given of the method for establishing two number toll calls between two automatic subscribers. 'VVhenan automatic subscriber desires a tollconnection toan automatic subscriber in another automatic exchange, the calling subscriberwill dialthe necessary digits to cause a rotary connector in his local exchange to connect with the connector bank contactso'fan idle trunkcircuit extending to the toll switchboard in the automatic exchange .l'iavingthe toll. switchroom. T he operator. at the toll switchboard is signalled in the well known manner and answers the call by inserting the answering plug of one of her cord circuits into theanswering ack of the trunk over which thecall is received. On receipt of the telephone number of the desired subscriber, she plugs into the call ack of a trunk circuit-extending to the automatic exchange in which the desired subscribers line terminates. The operator now-dials and operates the automatic switches in such exchange to complete the desired connection.

Having described in a general way the method of handling the two number toll calls, the operation of the circuits may now be explained in detail. For this purpose, it will be assumedthat an automatic subscriber in one of the automatic exchangesdesires to converse with an automatic subscriber whose line terminates in an automatic enchange located in an adjacent village or town. The calling party dials the proper digitsto trunk the call through the automatic switches in the automatic exchange in which the call originates in order to seize an idle trunk circuit, which we will assume is the "trunk circuit TC extending to the toll switchboard in the toll switching center. WVhen the rotary connector seizes the trunk circuit TC which it does by way or bank contacts 46, 47 and 48, the switching relay 1'? of the line switch Lid and the-switching relay oft-he connector energize in series. By the operation of the cut-oil relay ot' the line switch LS, the line switch is prevented from operating and by the operation of the switching relay of the connector ringing current is applied to the til the-cut-oft relay 3 is energized.

upon energizing, closes a circuit for lighting the lamp L and for operating the visuals D.

It may well be mentioned at this time that the ring-up relay 2 when operated, mechanically locks itself in an operated position un- A relay combination and mechanically locking a1- rangement of this type are disclosed in Patent 1,532,891, issued April 7, 1925 to John Erickson.

The operation of the visual signals D at the various toll operators positions indicates to such operators that the trunk circuit TC is busy. The lighting of the lamp L at the answering tollposition indicates to the operator at such position that a subscriber. in one of the automatic exchanges desires'a toll connection.

The operator at the switchboardperceiving the lighted condition of the lamp L inserts the plug P (or P into the answering jack AJ of the trunk circuit TC. Responsive to the insertion of the plug P into the jack AJ a circuit is closed for energizing relay a of the trunk circuit TC and relay 300i the cord circuit CC in series over the sleeve conductors of the jack-AJ and plug P. Relay 4, upon energizing, closes a bridge including :armature l and coil 6 acrossthe trunk conductors of the trunk circuit TC for cutting ofi' the ringing current. At armatures 10 and 12, relay 4 removes the high resistance shunts and '16 from around the condensers O and C respectively, and at armature llcloses a circuit for energizing cut-off relay 3 in series with relay 5. Relay 3 is a little slow to :pull up and therefore relay 5 energizes first and at armatures 13 and 1a, the latter relay opens a point in the shuntcircuit around the high resistances 15 and 16 and the condensers C and C. Relay 3 energizes shortly after relay 5. Relay 3 at armatures 8 and 9 and their resting contact opens 'thecircuit of the ringup relay 2 and also opens the mechanically locking arrangement thereby permitting ring-up relay 2 to. release. At the working contacts of armatures 8 and?) relay 3 prepares a shunt circuit around the high resistances l5 and 16 andthe condenser C and O for a purpose which will be explained hereinafter. At a anature 7 and its resting contact relay 3 opens the circuit of the lamp L and at its working Contact closes .a circuit for maintainingthe visual signals Dat the various toll operators positionsin'busy condition. 7

The operator, atter plugging in throws her key K into listening position, thereby operating the left hand springs thereof so as to connectthe listening conductors 4.4 and-to her head set. She now converses with the distant automatic subscriber and finds out the telephone number of the desired subscribers line. Assuming that the calling automatic subscriber desires a connection to an automatic subscriber whose line terminates in distant automatic exchange, the operator inserts the plug P of the cord circuit CC into a multiple call jack DJ of a trunk circuit such as TC which extends to the distant automatic exchange in which the desired autom atic subscribers line terminates. The operated condition of the visuals D associated with the trunk circuits indicate to the operator the idle or busy condition of such trunk line thereby permitting the operator to plug into the ack of such a trunk line without the usual testing operation.

For convenience, it will now be assumed that the plug P has been inserted into the call jack DJ and that the circuit TC is now the trunk circuit extending to the automatic exchange in which the desired subscribers line terminates. When the sleeve contacts of plug P comes into engagement with the corresponding contact of the jack DJ a circuit is closed over the sleeve conductors of the plug P and ack DJ to relay 36 of the cord circuit CC in series with relays 3 and 5 0t the trunk circuit TC. Relay 36, however, being marginally adjusted, does not energize. It may well be mentioned at this time that relays such as relays 31, 32, 33, and 36 are not operated in two number toll calls and are only operated when connected with the toll transmission trunks which also terminate in the operators switchboard. In the trunk circuit TC the relays 3 and 5 are operated, relay 5,

however, operates slightly ahead of relay 3 and at armatures 13 and 14; opens a point in the shunt circuit around the resistances 15 and 16 and condensers C and C. Shortly after relay 5 energizes, relay 3 also energizes and at armatures 8 and 9 prepares points in the shunt circuits around the resistances 15 and 16 and the condensers C and C. At armature 7 and its working contact relay 3 connects ground to the visuals D at the various operators positions thereby indicating to the operators at such positions that the trunk circuit TC is in use.

The operator now restores her listening key K and throws her calling device key K in such a direction as to operate the right hand springs thereof. By the operation of the lower rigiit hand pair of springs of the key K the resistance 40, which heretofore had been short circuited, is now included in the energizing circuit of the relays 3 and 5.

Responsive to the insertion of the resistance 40 in the above mentioned circuit, relay 5, which is marginally adjusted releases and at armatures 13 and 14 completes the shunt circuit around the high resistances 15 and 16' and the condensers C and C. It should be mentioned at this time that the resistances 15 and 16 are of such high resistance as to render the line relay 18 ot the lineswitch LS inoperative thereby preventing the operation of the line switch LS and the occurrence of false impulses during the time the plug of the cord circuit is being inserted into the jack. However, as soon as the right hand springs or the dial key K are operated, a circuit may be traced ior energizi g the line relay 18 of the line switch LS as follows: from ground by way 0t resting contact of armature 21, lower talking conductor of the trunk circuit TC, armature 14c, armature 9 and its working contact, ring spring of jack DJ, ring contact oi? plug P resting springs of the lower ring key K working springs of the lower dial key K dial conductor 13, through the normally closed springs of the operators calling device, dial conductor 42, working springs of the upper dial key K resting springs of the upper ring kc K tip contact of plug P tip spring of jack DJ, working contact of armature 3 and said armature, armature 13, upper talking conductor of trunk TC, armature 19 and its resting contact, and winding of relay 18 to battery. Upon. energizing, the line relay completes at its armature 22 a circuit which extends through the switching relay 1? and the stepping magnet 19 in series to battery, and at its armature 23 connects the test wiper 25 to the above circuit at a point midway between the switching relay and the stepping magnet. The operation now depends upon whether the first selector trunk with which the wipers of the line switch are in connection is busy or not busy. If this trunk line is busy the test Contact will have a ground potential upon it, the switching relay will be short circuited, and the stepping magnet 19, which intcrrupts its own circuit, will operate as a buzzer to advance the wipers 24 to 26, inclusive, stepby-step in search of an idle trunk line. This operation will continue as long as the test wiper 25 continues to engage ground or busy test contacts.

Assuming that the first idle selector trunk is the trunk which terminates in the bank contacts 49 to 51, inclusi e, the test contact 50 associated with such trunk will therefore not be grounded. When the test wiper 25 engages the test contact 50 the switching relay 17, being no longer short circuited, energizes and disconnects the upper and lower trunk conductors of the trunk circuit TC from the-winding of the line relay and from ground, respectively, and extends the conductors by way of armatures 19 and 21 and their working contacts, wipers 24- and 26, bank contacts a9 and 51 to the upper and lower windings of the line relay of the selector (not shown) associated with the seizec trunk line. The line and release r lays of the selector operate and the latter relay connects O i. t

ground to the release trunk conductor thereby maintaining the switching relay 17 of the line switch in operated position. It is understood that the above holding circuit is completed before the slow acting relay 18 has had time to deenergize. In addition to mamtaining the switching relay energized, the holding circuit also serves to connect ground to the n'iultiples of the test contacts 50 and also to the multiple test contacts 47 which terminate in the bank of the rotary connectors which have access to thetrunk circuits such as TC, thereby guarding the connection against intrusion in the customary manner.

The operator now dials the digits of the called telephone number, thereby causing the automatic switches to operate in the well known manner and complete the-connection to the desired suhscribers line.

After dialling the desired subscribers telephone number the operator restores the dial key K and substitutes the bridge including the retard coil 3 and polarized relay 35 in place of the operators calling device. In addition, the resistance i is again short circuited by the lower springs of the dial key K thereby permitting relay 5 of the trunk circuit TC to again energize. Relay 5, upon energizing, at armature 13 and Vi, opens the shunt circuit around the resistances l5 and 16 and the condensers C and C. The condensers C and C, however, are shunted by the resistances and 16. The bridge for holding the automatic switches in energized position may be traced as follows: from ground through the lower winding of the line relay of the connector in use, through the lower talking conductors of the various operated automatic switches to wiper 26 of the line switch LS, armature 21, lower talking conductor of the trunk circuit TC, armature 12, high resistance 16, ring contact of jack DJ, ring Contact of plug P normally closed springs of the ring key K normally closed springs of the dial key K normally and resting contact of relay 36, lower winding of retard coil 34, polarized relay 35, upper winding of retard coil '34, normally closed sori s of the dial key K normally O closed springs of the ring key K tip contact of the plug P tip spring of the jack DJ, high resistance 15, armature 10, upper talking conductors of the trunk circuit TC, armature l9 and its working contact, wiper of the line switch LS, and through the upper talking conductors of the operated automatic switches to the upper winding of theline relay of the used connector and battery. The line relay of the connector is maintained energized over this circuit.

in the cord circuit CC, the polarized relay is energized over the above traced circuit and closes a circuit for lighting the lamp L The lighting of the supervisory lamp L indicates to the operator that the connector is wee-.

ringing thecallecl party and that such party has not yetanswered.

When the called party answers, responsive to ringing current-applied by the connector switch, which is the last switch operated by the operator, the back bridge relay in such connector switch energizes and reverses the direction of current flow in the upper and lower talking conductors of the trunk circuit TC in the regular way. The flow of current is now in such direction as to cause relay 35 in the cord circuit CC to deenergize. P0- larized relay 35 therefore deenergizes and opensthe circuit of the supervisory lamp L thereby notifying the operator that the called party has answered. The calling and called party may now converse with each other as desired.

Upon the termination of conversation and responsive to the hanging up of the receiver by the callea party, the back bridge relay of the connector releases and reverses the current flow over the upper and lower talking conductors of the trunk circuit TC so that the polarized relay again energizes. Relay 35 again closes the circuit for lightingthe supervisory lamp L thereby notifying the operator that the called party has hung up his receiver. The operator, upon observing the lighted condition of lame L removes the plug P from the jack DJ thereby opening the circuits of relays 3 and 5 whereupon said relays deenergize. By the removal of the plug P from the jack DJ, the holding bridge across the trunk circuit TC extending to the operated automatic switches is opened and the automatic switches release in the well known manner. The trunk circuit TC extending to the automatic exchange in which the called subscribers line terminates and the automatic switches including the lineswitch LS in such automatic exchange are now in their normal position and may be used for extending other calls.

The operator now removesthe plug P from the jack AJ of the trunk circuit TC, which extends to the automatic exchange in which the calling subscribers line terminates. Responsive to the removal of the plug P from the jack AJ, the circuit of relay 30 in the cord circuit CC and relay l in the trunk circuit is opened, whereupon said relays deenergize. At armature 11, relay l opens the circuit of relays 3 and 5 whereupon said relays deenergize. At armature 10, relay 4 opens the holding bridge across the trunk circuit TC whereby the connector which is in engagement with the bank contacts 46, 4:7, and 4-8 is prepared for release in the well known manner. When the calling party hangs up his receiver, the automatic switches in the automatic exchange release in the Well known manner. The trunk circuit TC, extending to the automatic exchange in which the calling subscribers line terminates is now in normal position and may be used for extending other calls.

From the foregoing it can be seen that when a trunk circuit such as TC is used for extending an outgoing call, the jack AJ is used for talking and supervisory purposes and the shunt around the condensers C and G is opened to separate the battery feed extending from the two connectors, one in the originating automatic office and the other in the terminating automatic oflice. hen the trunk circuit such as TC is used for extending a call to a called party the multiple calling or dialling jack such as DJ is used for extending the call and the circuit arrangement is such that the condensers and the high resistances 15 and 16 are shunted out during dialling and only the condensers C and C are shunted out during the talking period by including the resistances 15 and 16 in shunt of such condensers for supervisory purposes.

Calls to automatic subscribers whose lines terminate in the automatic exchange associated with the toll switching center are completed in the same manner as previously ex plained except that the plug of the cord circuit CC is inserted into a local jack leading to the local automatic trunking arrangement.

The cord circuit CC is also adaptable to be used in connection with the toll transmission switches for completing long distance calls to more remote points than the automatic exchanges located within this specific switching area.

Having described the invention, its utility and operation, what is considered new and is desired to have protected by Letters Patent will be set forth in the appended claims.

What is claimed is:

1. In a telephone system, a two-way trunk circuit having an individual answering ack and a plurality of multiple call jacks connected in multiple with said answering jack, a cord circuit, circuit arrangements in said trunk circuit requiring different adjustments for incoming and outgoing service and means for automatically adjusting said circuits dependent upon which jack said cord circuit is plugged into.

2. In a telephone system, a two-way trunk terminating in an individual answering ack and a plurality of multiple call jacks, an individual sleeve conductor for said answering jack and a sleeve conductor for said multiple call jacks, a cord circuit, and relays in said trunk circuit controlled over said sleeve conductors for automatically adjusting said trunk circuit for either incoming or outgoing service dependent upon which jack said cord circuit is plugged into.

3. In a telephone system, a two-way trunk line terminating in one end in a toll switchboard and in the other end in an automatic switch, condensers in the talking conductors of said trunk line, a cord circuit at said switchboard, means for closing a bridge across the talking conductors of said trunk line when said cord circuit is connected with said trunk line, high resistance shunt circuits normally closed around the said condensers, said shunt circuits being of such resistance so as to prevent the operation of said switch, and means in said trunk line for closing low resistance shunt circuits around said condensers and said high resistance shunt circuits to start the operation of said switch. 4. In a telephone system, a two-way trunk line, two condensers inserted in the two talking conductors of said trunk line, respectively, high resistance shunt circuits normally closed around said condensers, means for opening said shunt circuits when said trunk line is used for extending an incoming call, and means for closing low resistance shunt circuits around said condensers and said high resistance shunt circuits during the dialling operation when said trunk line is in use for extending an outgoing call.

5. In a telephone system, a two-way trunk line, two condensers inserted in the two talking conductors of said trunk line, respectively, high resistance shunt circuits normally closed around said condensers. means for opening said shunt circuits when said trunk line is used as an incoming trunk line, and means for closing low resistance shunt circuits around said condensers and said high resistance shunt circuits during the dialling operation in extending a call and for subsequently opening said low resistance shunt circuits thereby including said high resistance shunt circuits in said trunk line when said trunk line is used as an outgoing trunk line.

6. In a telephone system, a two-way trunk line, two condensers inserted in the two talking leads of the trunk circuit, respectively, a relay in said trunk line, high resistance shunt circuits normally closed around said condensers, means for operating said relay to open said high resistance shunt circuits when said trunk line is used for extending an in coming call, a second and a third relay in said trunk circuit, and means for energizing the said second and third relays and then deenergizing said third relay during the dialing operation to place low resistance shunt circuits around said condensers and said high resistance shunt circuits when said trunk circuit is used for extending an outgoing call.

7. In a telephone system, a two-way trunk circuit terminating in an individual answering ack and a plurality of multiple call jacks, an individual sleeve conductor for said answering jack and a sleeve conductor for said multiple call jacks, a relay having a circuit including the sleeve conductor of said answering 'ack, two condensers inserted in the two talking leads of said, trunk circuit,

respectively, high resistance shunt circuits normally closed around said condensers, a cord circuit, said relayoperated responsiveto the insertion of a plug of said cord circuit into said answering ack for opening the high resistance 7 shunt circuits around said. condensers when said trunk circuit istaken into use for an incoming call, a second .anda third re,- lay in said trunk circuit having a circuit in cluding the sleeve conductor of said call jacks, said second and third relaysoperated responsive to the insertion of saidcord circuit into one ofsaid call jacks, a dialkey in said cord circuit, and means responsive to the operation of said dial key for maintaining said second relay .operatedand for causing said third relay to deenergizeand place low resistance shunt circuits around said .condensers and, high resistance shunt circuits when said trunk circuit isused in extending an outgoing call.

8; In a telephonesystem, a two wa-ytrurik line and a cord circuit for use in setting .up connections v1n two directions, condensers in said trunk lined-for stoppingcurrent flowrover' said trunk line when said trunlrlinetand cord circuit arein-use ina connectionset'upin one direction, andmeans for short-circuiting. said condensers toopermitcurrent/flow over the trunk line when said trunk line and cord circuit are in use in ft-CODIIGCtlOIL set up in the opposite direction.

9. In .a telephone system, means including two similar two-way trunk lines :and a cord circuit or setting up connections inopposite directions, condensers in said trunk lines, means whereby the condensers in .the first-of said trunk linesare short-circuitedto permit current flow while the condensers in:

the second trunk line stop thecunrent flow in a connection set up in: one direction, andmeans whereby the condensers -1n thesecond:

trunk line are short-circuited to permit current flow while the condensers in the first trunk line stop thecurrentifiow ,ina connection set up in a'difierent-di rection.

In witness whereof I hereunto subscribe my name this lZth day of March, 1927,.

THOMAS F; CROGK'ER. In Witness whereof I hereunto subscribe my name this 17th day 01": March, 1927.

HARRY PARSHALL. 

